FirebaseMessaging is null null and SendMessage fails because of it

Question

I have a code here where I want to use FireBase Admin to send push notifications to IOS and Android. I recieve token, title and body from method.

var message = new FirebaseAdmin.Messaging.Message()
                {
                    Notification = new FirebaseAdmin.Messaging.Notification
                    {
                        Title = title,
                        Body = body
                    },
                    Token = DeviceToken.First(),
                    Apns = new ApnsConfig { Aps = new Aps { ContentAvailable = true, Sound = "default", Category = "test" } },
                    Android = new AndroidConfig { Notification = new AndroidNotification { ClickAction = "test" } }
                };

                var messaging = FirebaseMessaging.DefaultInstance;

                await messaging.SendAsync(message);